The invention relates generally to imaging devices for detecting radiation distribution by a scintillation camera. The invention relates particularly to a stand for adapting a conventional scintillation camera for emission computed axial tomography analysis of a patient.
In a scintillation camera adapted for trans-axial tomographic scanning, a scintillation detector precesses in an orbit about a patient having an axis of precession corresponding to the cranial-caudal axis of the patient. The scintillation detector head employs an array of photodetectors viewing overlapping portions of a scintillation crystal which is formed in the shape of a disk. Radiation impinging upon the crystal, which is typically formed of sodium iodide, causes flashes of light to be emitted which are detected by photomultiplier tubes viewing the area of emission. The photomultiplier tubes generate electrical signals proportional to the magnitude of the light intensity received. These signals are matrixed together to provide positional information, thereby locating the point of origin of the scintillation in the plane of the crystal. If a collimator is interposed between the radiation source and the detector crystal, the location of the scintillation will correspond to the point of origin in the patient of the incident gamma ray causing the scintillation. This point is then depicted in a two-dimensional matrix. This brief description of the operation of a scintillation camera is adequate for purposes of this invention, as the basic principles are explained at length in U.S. Pat. No. 3,011,057.
In trans-axial tomographic scanning, a radiation detector is moved in an orbit about a subject of interest rotating to face the subject of interest at all times. Typically, the subject of interest is a human patient and the orbit in which the radiation detector moves is a circular orbit in which the axis of the circle about which the detector precesses is referred to as the cranial-caudal axis. The scintillation detector is always tangent to this circle.
In trans-axial tomographic scanning a single precession of a scintillation camera detector about the patient produces an image showing the radioactive distribution in a plurality of section imaging planes, which are transverse planes that are mutually parallel and usually perpendicular to the cranial-caudal axis. Gamma rays eminating both from within and from without these planes are detected. Detected radiation producing scintillations in the crystal detector is associated by computational and storage means with the nearest section imaging plane. The motion of the scintillation camera detector about the cranial-caudal axis is digitized and represented in electronic form in a computation means, such as a small computer. Using an appropriate algorithm, the computer concurrently determines the distribution of radioactive events within a plurality of parallel section imaging planes typically having a thickness of about 2 centimeters. The computed radioactive distribution is displayed on a visual image display device. Precession continues for imaging in the section imaging plane until the scintillation detector has moved 360.degree. about the cranial-caudal axis. In theory, a precession through only 180.degree. would be practical, but precession through 360.degree. is performed to minimize internal attenuation effects insofar as is possible. While precession of the detector is preferably, a continuous advancement through the detector orbit data registration within a particular imaging frame is performed in discrete counting intervals which are initiated and terminated in step-wise increments.
A particular problem associated with emission computed axial tomography is that the orbiting structure and mechanism are usually quite elaborate and expensive, and also require unique detector heads. Examples of such structures are shown in U.S. Pat. Nos. 4,057,726 and 4,057,727. The use of such structures is also limited to the mode of axial tomography analysis and the structure can not be efficiently used for conventional stationary radiation distribution analysis of a patient.
Accordingly, one object of the present invention is to provide a structure in which a conventional, counterbalanced scintillation camera can be used for emission tomography.
Another object of the present invention is to provide a structure in which a conventional, counterbalanced scintillation camera can be utilized for either emission tomography or conventional stationary radiation distribution analysis.